Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$131.58	3.814%	$136.5985	$136.60	$136.60	$136.60
Purchase #2	$52.66	9.356%	$57.5869	$57.59	$57.60	$57.60
Purchase #3	$143.26	11.853%	$160.2406	$160.24	$160.25	$160.20
Purchase #4	$35.95	3.820%	$37.3233	$37.32	$37.30	$37.30
Purchase #5	$105.81	5.750%	$111.8941	$111.89	$111.90	$111.90
Purchase #6	$53.41	3.163%	$55.0994	$55.10	$55.10	$55.10
Purchase #7	$115.31	4.266%	$120.2291	$120.23	$120.25	$120.20
7 purchase totals =	$637.98		$678.9719	$678.97	$679.00	$678.90